At present, more than 80% of the use of lead is for lead-acid batteries. With the popularization of automobiles and the development of new energy industries, the use of lead-acid batteries is increasing, and the scrapped lead-acid batteries are mounting. Metallurgical researchers and environmentalists have done extensive research on how to dispose waste batteries in a simple, economical, scientific and environmental way. Especially, in the face of increasingly stringent environmental requirements, the wet smelting of lead is imperative. The technology of dismantling waste batteries has developed rapidly. The breakage and disassembling of batteries have achieved large-scale modern production, and the plastic boxes and conductive plate grid materials have been effectively recycled. However, the treatment of lead paste/mud of the batteries is still performed by fire smelting process. The lead in the lead paste/mud mainly includes PbSO4, PbO2, PbO, and a small amount of metal lead; and the other additives added when manufacturing the batteries, such as barium sulfate, carbon core and organic additives, are also included in the lead paste/mud. When the lead paste/mud is treated by the fire method, harmful substances such as lead dust, sulfur dioxide, and dioxins are inevitably generated to cause serious pollution to the environment. The clean and environment-friendly treatment of lead paste/mud is still an urgent issue to be solved.
For this purpose, a lot of research has been carried out to try to replace the fire treatment method with an environment-friendly and economical hydrometallurgical method. However, due to the complex phase composition of the paste/mud, currently, there is no wet treatment method that can compete with the fire method in terms of economy, cost, energy consumption and environment protection. Therefore, the treatment of lead paste/mud is still achieved by the fire smelting process; and some of the treatment processes include the desulfurization with ammonium bicarbonate or sodium alkali prior to the smelting by the fire method, and then the reduction and smelting are performed using the fire method.
A lot of research has been done on the wet treatment of lead paste/mud. The wet treatment of lead paste/mud mainly includes three methods. The first method is treatment by a solid phase reduction method, which is represented by the solid phase electrolysis researched by Keyuan Lu et al, Institute of Chemical Metallurgy, Chinese Academy of Sciences. The characteristic of this method is that the electrolysis is carried out in a NaOH solution, including the following steps. First, the paste/mud is converted with NaOH (electrolytic residue), specifically the PbSO4 is converted into Pb(OH)2 and sodium sulfate, and after the conversion, the converted lead paste/mud is dehydrated and then coated onto a special cathode plate; then PbO2, Pb(OH)2, and PbO are reduced to metal lead at the cathode, and O2 is generated at the anode; and the solution containing sodium sulfate is discharged after being treated. The second method is an electrowinning method, which is mainly characterized in that, the lead is dissolved to form a soluble lead salt solution, and a direct current is passed through the electrolytic bath; the lead in the solution is precipitated at the cathode, and oxygen and PbO2 are generated at the anode. The electrolyte solution used is silicofluoric acid, borofluoric acid, sodium hydroxide solution, perchloric acid solution, etc. The third method is to make lead paste/mud into lead compounds, such as lead oxide, lead chloride, etc.
The above various wet treatment methods for treating the paste/mud of waste lead battery are economically impossible to compete with the current fire smelting process. Therefore, the treatment of lead paste/mud, at home and abroad, is still achieved by using the fire smelting method.
In addition, the raw materials and the secondary resource of zinc for smelting zinc by wet treatment method contain lead, and this lead eventually remains in the zinc leaching slag in a form of lead sulfate. At present, such materials are smelted by fire method to recover the lead from them, which not only consumes high energy, but also causes serious pollution to the environment due to the generated harmful substances such as lead dust, sulfur dioxide and dioxins during the smelting process.